The formation of calcified tissue is essential for the development and survival and vertebrates. At present, the signal transduction mechanisms involved in calcium regulation in biomineralized tissue such as dentin and tooth enamel are poorly understood. We recently made the exciting discovery that odontoblast membranes of rat maxillary incisor teeth express extremely high levels of inositol 1,4,5-triphosphate (IP3) receptors and a related GTP binding regulatory protein. In this application, we propose to investigate IP3 receptor expression and function in rat odontoblasts. IP3 receptor expression will be examined in odontoblast cells of different developmental stages found within mandibular rat incisors. The temporal expression of this receptor in relation to the formation and deposition of dentin will be examined to suggest a functional role for this receptor in odontoblasts. Then, functional studies will examine calcium release in an odontoblast cell line. In many cells, the activation of cell surface receptors elevates cytosolic calcium from internal membrane stores of odontoblasts may be a tightly regulated source of calcium for mineralization of dentin. Intracellular agonist such as IP3 may regulate this calcium release during dentin-ogenesis. The second aim of this proposal is to examine internal membrane stores of calcium that may be gated by IP3 in an odontoblast- derived cell line. These studies will qualitatively examine internal membrane stores of calcium that may be gated by IP3 in an odontoblast- derived cell line. These studies will qualitatively examine internal membrane stores of calcium during mineralization in odontoiblast- derived MDPC-23 cells. These studies will further examine calcium entry through plasma membrane channels in relation to calcium storage within internal membranes. Finally, the ability of exogenous agonists to stimulate IP3 turnover and calcium flux in MDPC-23 cells will be examined. This study will provide a basis for more fully understanding the underlying physiology of dentin formation. This study will also have an impact on other biomineralization processes such as enamel formation and vertebrate bone development. Finally, this proposed research will further the development of odontoblasts and an odontoblast cell line as models for understanding the proposed role of IP3 on calcium-mediated secretion.